This invention relates generally as indicated to a limited angle torque motor with high stiffness and natural frequency.
The motor of the present invention is desirably generally of the type disclosed in copending U.S. application Ser. No. 579,784, filed Feb. 13, 1984, now U.S. Pat. No. 4,510,403 the disclosure of which is incorpoarated herein by reference. Such motor is particularly suited for use in certain types of high pressure fluid proportional servo control systems including, but not limited to, aircraft controls to drive a proportional control valve of relatively short stroke. The fluid pressure is normally on the order of 1,000 psi or more.
In such a motor, the magnetic reluctance torque of the motor can be controlled within certain limits to obtain a particular desired inherent magnetic centering spring rate at a particular torque or power level. However, such a motor has a somewhat limited magnetic spring capability inherent in the design, and there are some applications in which it is desirable for the motor to have a higher centering spring gradient to increase the dynamic stiffness of a servo system as where the motor is being used to drive a load having substantial and varying force levels.
Such a motor also has a torsional undamped natural frequency which is generally related to the magnetic spring rate through the center position and rotational inertia of the rotor. Typically such natural frequencies have been limited to about 60 Hertz (Hz) for motors of practical design. However, for certain high response servo sustem applications, it is desirable to have a substantially higher motor natural frequency, on the order of 75 to 100 Hz or more.